1. Field of the Invention
The present invention relates to semiconductor substrates, and more particularly, to a semiconductor substrate and a fabrication method thereof for preventing distortion of high frequency signals.
2. Description of Related Art
Along with the rapid development of electronic industries, electronic products are developed towards miniaturization, high electrical performance, high functionality and high speed. Accordingly, three-dimensional chip stack technologies have been developed, which generally involve RDL (redistribution layer) structures, TSV (through silicon via) structures, etc. for forming electrical connection structures for signal transmission so as to increase operation speeds and bandwidths of chip stack structures.
FIGS. 1A to 1C are schematic cross-sectional views showing a fabrication method of a conventional semiconductor substrate 1.
Referring to FIG. 1A, a silicon-containing substrate body 10 having a plurality of through holes 100 formed therein is provided. The substrate body 10 is further heated in an oxygen environment so as to cause upper and lower surfaces of the substrate body 10 and walls of the through holes 100 to be made of an insulating material 11 of silicon dioxide.
Referring to FIG. 1B, a metal material is filled in the through holes 100 to form TSVs 13, and a circuit layer 12 is formed on the upper surface of the substrate body 10 and electrically connected to the TSVs 13. Therein, portions of the circuit layer 12 can serve as integrated passive devices (not shown).
Referring to FIG. 1C, an RDL structure 14 is formed on the upper surface of the substrate body 10, the circuit layer 12 and the TSVs 13. Further, an insulating layer 15 is formed on the RDL structure 14 and a plurality of openings 150 are formed in the insulating layer 15 so as for a plurality of conductive elements 16 to be formed in the openings 150.
The insulating material 11 of silicon dioxide is formed by heating the substrate body 10 in a high temperature and high pressure environment for a certain time duration. Generally, a thin insulating material is formed with a short heating time so as to reduce the fabrication cost. As such, referring to FIG. 1B, the distance between the circuit layer 12 and the substrate body 10, i.e., the thickness t of the insulating material 11, becomes very small, thus easily resulting in signal degradation when high frequency signals are applied to the circuit layer 12.
On the other hand, in order to increase the thickness of the insulating material 11 so as to overcome the above-described drawback, both the heating time and the concentration of oxygen need to be increased, thereby greatly increasing the fabrication cost.
Therefore, there is a need to provide a semiconductor substrate and a fabrication method thereof so as to overcome the above-described drawbacks.